Recently, much attention has been paid to organic light-emitting devices such as organic EL devices that can be easily applied to a surface light-emitting device. Specifically, the organic light-emitting device has been considered to be useful as an economical, solid emission type, light-emitting device having a large emission area such as a full color display device and a writing light source array, thereby having been actively studied. The organic light-emitting device generally comprises a couple of electrodes, a transparent electrode and a back side electrode, and a light-emitting organic thin film disposed between the electrodes. When to the organic light-emitting device is applied an electric field, electrons are injected from the back side electrode and holes are injected from the transparent electrode to the light-emitting organic thin film. The electrons and the holes are re-combined in the light-emitting organic thin film and energy is converted into light while an energy level is turned from a conduction band to a valence band, whereby the organic light-emitting device emits light.
The organic thin film in the organic light-emitting device has been generally provided by a vapor deposition process. Patterning methods for the organic thin film have been proposed in view of development of color image emission. For example, U.S. Pat. No. 5,294,869 disclosed a patterning method using a shadow mask. However, this patterning method needs a complicated vapor deposition apparatus to be poor in productivity and positional accuracy of patterning.
To overcome the above problems in patterning, Japanese Patent Laid-Open No. 9-167684 disclosed a method where an organic thin film is uniformly provided on a mica temporary substrate by a vapor deposition process beforehand, and the organic thin film is disposed closer to a substrate and selectively vapor-deposited onto the substrate in a pattern. Further, Japanese Patent Laid-Open No. 2000-195665 disclosed a method where an organic thin film is uniformly provided on a film temporary substrate by a vapor deposition process beforehand, and the organic thin film is disposed closer to a substrate through a mask and vapor-deposited onto the substrate in a pattern of the mask. These methods using the vapor deposition source provided on the temporary substrate are disadvantageous in that the vapor deposition process is poor in productivity and that only a low molecular weight organic compound can be used for the organic thin film.
Polymer-type organic light-emitting devices using a light-emitting organic thin film made of a polymer or a low molecular weight organic compound dispersed in a binder resin also have been known. Examples of the polymer include poly(p-phenylenevinylene) for green light emission (Nature, Vol. 347, Page 539, 1990), poly(3-alkylthiophene) for red-orange light emission (Japanese Journal of Applied Physics, Vol. 30, Page L1938, 1991), polyalkylfluorene blue light emission (Japanese Journal of Applied Physics, Vol. 30, Page L1941, 1991), etc. Such polymer-type organic light-emitting devices can be easily increased in emitting area to be useful for a flexible device. However, the light-emitting organic thin film cannot be provided by a vapor deposition process, whereby the light-emitting organic thin film is generally provided by a wet method.
As a method for providing a patterned, light-emitting organic thin film of the polymer-type organic light-emitting device, an ink-jet method, a printing method, etc. have been proposed. However, the patterned, light-emitting organic thin film provided by such a method is insufficient in uniformity of thickness because of a surface tension of a solution used in the method. Further, in the case of providing a laminate of a plurality of organic thin films, components is dissolved and mixed around a boundary of each film. Thus, the polymer-type organic light-emitting device utilizing the patterning method is poor in light-emitting efficiency and durability.
Expectations are high for a plastic film of a high molecular weight material as a flexible substrate of the organic light-emitting device. However, the plastic film is poor in oxygen- and water-resistance to be far from practicable, so that the substrate is generally made of a glass. The glass substrate is more difficult in handling than the plastic film, thereby reducing productivity in wet method. Further, in the case of using the plastic film substrate, the transparent electrode and a thin film transistor are laminated on the substrate to be costly. Coating such a substrate with the organic thin film is disadvantageous in yield and economical efficiency. Thus, there has been increasing need for a patterning method usable for production of the polymer-type organic light-emitting device.
WO 00/41893 disclosed a method using a donor sheet comprising an organic thin film and a photo-thermal conversion layer, where the organic thin film is thermally transferred to the substrate in a desired pattern by a laser. Such a thermal transfer method is disadvantageous in that a gas often penetrates into an interface between the organic thin film and the substrate. In the organic light-emitting device produced by this method, light-emitting efficiency, durability and uniformity of a light-emitting surface depend on conditions of the interface, and light-emitting properties are worsened by the penetration of a gas.
Further, in thermal writing-patterning method using a thermal head or a laser that is utilized in printing technique, temperature distribution expands around the pattern due to thermal diffusivity so that outlines of the organic thin film cannot be formed accurately. Thus, organic light-emitting devices produced by this method vary in amount of emission and has a defect due to an electric inferiority or a break of the organic thin film to be poor in durability. Further, there is a case where yield is lowered by poor positional accuracy of the substrate and the thermal head or the laser.